1. Field of the Invention
The present invention relates to a display device which is manufactured by using an element having a light emitting material interposed between electrodes and emitting light by applying an electric current between the electrodes (light emitting element).
2. Description of the Related Art
In recent years, a thin lightweight display using a light emitting element has been actively developed. The light emitting element is manufactured by interposing a material which emits light by applying an electric current between a pair of electrodes. Since the light emitting element itself emits light unlike in the case of liquid crystal, a light source such as back light is not required, and the element is very thin. Therefore, it is extremely advantageous to manufacture a thin lightweight display.
However, one background of not reaching practical use yet while having such big advantages is a problem of reliability. The light emitting element often deteriorates due to moisture (water) and has a disadvantage of being hard to obtain long-term reliability. The light emitting element which is deteriorated due to water causes a decrease in luminance or does not emit light. It is conceivable that this causes a dark spot (black spot) and shrinkage (a decrease in luminance from an edge portion of a display device) in a display device using the light emitting element. Various countermeasures are suggested to suppress such deterioration (for example, Reference 1: Japanese Patent Laid-Open No. H9-148066, and Reference 2: Japanese Patent Laid-Open No. H7-169567).
However, these countermeasures are insufficient and have few effects on a defect that a region where emission intensity is decreased is gradually increased with time. A major reason for such a defect is an influence of water remaining inside a light emitting device besides water entering from outside. Additional countermeasures are desired.